Abstract
Throughout Einstein’s research on quantum theory he distinguished between the emission and absorption of radiation by describing them as separate physical processes. Absorption is described as a continuous process acting upon the resonator (quantum oscillator) by means of electromagnetic fields, while emission is described as occurring in integral steps due to the localization and release of discrete energy packets. We follow this aspect of his research as it develops by highlighting passages from his papers published between 1905 and 1917. We reveal in detail why he opposed the standard interpretation by comparing his unfinished theory to that of non-relativistic quantum mechanics which uses the wave function to describe the emission and absorption of radiation as a single process. We show that the conflict between his theory and non-relativistic theories can be resolved by deriving a Lagrangian theory of quantum mechanics.